1. Field of the Invention
The present invention relates to a method of recording an image which makes it possible to display a multiplicity of colors with a multiplicity of gradations by making dot pitches with respect to the separation of each color relatively variable among various colors.
2. Description of the Related Art
As a means for obtaining a recording of a multiplicity of colors with a multiplicity of gradations, it is possible to cite, for example, the halftone dot gradation representation for representing a desired gradation by making each halftone-dot area variable in correspondence with the gradation. In this case, a recording is effected by superimposing dots of respective colors having identical shapes one on top of another so as to cope with a multicolor recording. However, in the event that a misregistration should occur for each recording, color moire would result.
To avoid the aforementioned color moire, it is possible to cope with the problem by improving the mechanical accuracy. However, since a technical difficulty is involved, the color moire is avoided in fields such as offset printing by varying the angle of arrangement of dots for each color. That is, instead of arranging the dots regularly in grid form, the angle of arrangement of the dots with respect to the main scanning direction is changed by 15.degree., 30.degree., 45.degree., or 75.degree..
Also, a means is known for suppressing the color moire by means of random dots, which are free of directionality for each color, by adopting the so-called FM screening in which dots of a predetermined size are arranged at random in correspondence with a gradation.
The above-described means is capable of effectively suppressing the occurrence of color moire in a case where dot pitches in the main scanning direction and subscanning direction can be set to be smaller than a minimum unit area in image processing which is dependent on an image processor of an image recording apparatus. However, in the case of line heads, such as a thermal head, a liquid-crystal head, a light-emitting diode (LED) head, and an electroluminescence (EL) head, in which the dot pitch in the main scanning direction is restricted by the size of a recording element and is substantially set to the aforementioned minimum unit area, the degree of freedom in the change of the dot pitch is limited to the subscanning direction. Accordingly, it is not possible to suppress moire fringes effectively.
To overcome the above-described situation, a method of recording a color image disclosed in Japanese Patent Application Laid-Open No. 5-155057 has been proposed. According to this method, respective pixels of the three primary colors are alternately offset by about 1/2 pitches in the subscanning direction so that the pixels of the three primaries are not arranged linearly in the main scanning direction, and the pixel length of one of the three primaries in the subscanning direction is set to be 1/2 of the pixel length of the other colors. As a result, even if a misregistration occurs, color patterns in two adjacent rows are maintained in a relationship of complementary color. Hence, the entire tone of color does not change, and it is possible to make the irregularity in color less conspicuous. However, even in the case where the multiplicity of colors are represented with the multiplicity of gradations by changing the angle of arrangement of halftone dots, it is difficult to obviate the occurrence of color moire which is called a rosette pattern which constitutes a factor for harsh texture.
In addition, according to the method of recording a color image disclosed in JapaneEe Patent Application Laid-Open No. 5-155057, even in the case where the dot pitch in the main scanning direction is limited, the color moire can be suppressed effectively in the case of three colors. This being the case, however, it is difficult to obviate the color moire which occurs in a case where a multiplicity of colors are recorded with a multiplicity of gradations through the four-color separation which is widely adopted in printing or graphic arts.
To overcome the above-described situation, a method of recording a color image disclosed in Japanese Patent Application Laid-Open No. 7-312677 (hereinafter referred to "Prior Invention") has been proposed.
In accordance with a first aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, wherein the pixel for each of the colors is constituted by a dot and/or a blank, the dot having a substantially fired shape and a variable density, and/or the dot having a substantially fixed density and a variable shape, comprising the steps of: recording one color with an arrangement pattern having a particular fixed dot pitch; and recording at least two of the colors with respective patterns in which dot pitches in the subscanning direction are set to mutually different fractional multiples of the dot pitch of the one color.
In accordance with a second aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the step of: setting a dot pitch ratio of colors of yellow, magenta cyan, and black to 1:0.75:0.60:0.50 in random order.
In accordance with a third aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the steps of: recording the colors with respective patterns in which dot pitches in the subscanning direction are set to mutually different fractional multiples of the dot pitch of one particular color; and increasing the dot pitch in the main scanning direction of one or more colors to lower a resolution in the main scanning direction of the particular color.
In accordance with a fourth aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the step of: recording each of the colors with a pattern having a dot pitch in which dots are arranged randomly in the subscanning direction.
In accordance with a fifth aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the steps of: recording one color with a dot arrangement pattern having a particular fixed dot pitch; and recording another color with a dot arrangement pattern having a dot pitch in which dots are arranged randomly in the subscanning direction.
In accordance with a sixth aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the steps of: recording yellow with a pattern having a dot pitch in which dots are arranged randomly in the subscanning direction; and recording magenta, cyan, and black with respective fixed dot pitch patterns in which dot pitches in the subecanning direction are set to mutually different fractional multiples of the dot pitch of yellow.
In accordance with a seventh aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magenta, cyan, and black, comprising the step of: setting dot pitch ratios of colors of yellow, magenta cyan, and black in the main scanning direction and the subscanning direction to 2:1:2:1 and 1:0.75:0.60:0.50, respectively.
In accordance with an eighth aspect of the Prior Invention, there is provided a method of recording an image in which a multicolor image is recorded by moving in a subscanning direction a head having a plurality of recording elements arrayed in a main scanning direction to make variable a density or an area ratio of each recording pixel in correspondence with a density of an original image, and by combining colors of yellow, magneta, cyan, and black, comprising the step of: setting dot pitch ratios of colors of yellow, magenta cyan, and black in the main scanning direction and the subscanning direction to 2:2:1:1 and 1:0.60:0.75:0.50, respectively.
In accordance with a ninth aspect of the Prior Invention, the method of recording an image according to the seventh aspect of the invention may further comprise the step of: consecutively executing in a predetermined pixel cycle a resolution conversion operation in which a resolution in the subscanning direction in color separation of yellow, magenta, cyan, and black each having a predetermined resolution is converted by interpolation processing, and a mask operation in which masks each having a predetermined pattern are superimposed on respective color-separated images with resolutions thereof converted, and a value of gradation data of the pixel which overlaps with the predetermined pattern among the pixels is set to a 0 so as to extract gradation image data of the respective colors.
In accordance with a 10th aspect of the Prior Invention, the method of recording an image according to the ninth aspect of the invention may further comprise the steps of: performing pattern processing in which gradations of the pixels of each of the colors are allotted to elements of a submatrix which is arranged in the subscanning direction in a unit of two pixels after the resolution conversion operation; and performing cancellation processing in which a predetermined number of low-order bits of the gradation data of each of the pixels before or after the mask operation.
In accordance with an 11th aspect of the Prior Invention, the method of recording an image according to the 10th aspect of the invention may further comprise the step of: determining the number of factors of the submatrix in accordance with the value of the gradation data.
In accordance with a 12th aspect of the Prior Invention, the method of recording an image according to the ninth aspect of the invention, in the mask operation gradation data having a maximum value is extracted with respect to an image in which the value of the gradation data has a maximum value.
The Prior Invention enables effective suppression of the color moire and vertical fringes even in the case where the dot pitch in the main scanning direction is structurally fixed. However, because the dot pitch of yellow in the subscanning direction is larger than that of other colors (for example, it is two times larger than that of black which is the minimum pitch), the peak recording temperature increases in case of recording 100% density dot, resulting in over heat of the center portion of the recording dot, which causes deterioration of the recording material and deformation of the base, therefore makes it difficult to perform fine recording.